Conventional methods for synchronizing reference vibration systems are summarized in the following two methods: that is, (1) preparing one reference vibration generating system and setting a distance between system units for transmitting and receiving signals to a constant value, to thereby realize synchronization between transmission and reception, and (2) detecting a phase difference between a transmission wave and a reception wave from one system unit to another, incorporating a circuit for adjusting the reference vibration, to thereby realize synchronization between transmission and reception. In a case of multiple system units, these methods are used in multistage.
In order to built a large-scale system with a large number of small-scale, low-priced systems and to make its ability exhibited at most, it is indispensable to realize synchronization between the small-scale systems so as to enable joint operation.
However, technical difficulties for solving delays increase rapidly with an increase in the number of system units in the aforementioned methods of synchronization due to their configuration.
Techniques for solving such problems are disclosed in the Japanese Paten Application Laid-open No. 10-262036 and the Japanese Patent Application Laid-open No. 2000-13217.
The technique disclosed in the Japanese Patent Application Laid-open No. 10-262036 has such a configuration that, by using a synthetic wave consisting of a received wave from another system unit and a transmission wave transmitted by itself as an input and setting the upper limit value and the lower limit value to the amplitude of the input wave, a reference vibration generating circuit system, which applies modulation to the transmission wave used as an output so as to put the input wave within the range, is added to each system unit. With this configuration, high-speed synchronization among system units of any numbers arranged distributively can be realized.
The technique disclosed in the Japanese Patent Application No. 2000-13217 has such a configuration that synchronization is performed in a combined circuit where plural oscillation circuits are combined due to mutual induction.
However, in the case of the technique disclosed in the Japanese Patent Application Laid-open No. 10-262036, synchronization is realized only when a phase difference exists between the received wave received from another system unit and a transmission wave transmitted by itself in the initial state. This is not so configured that synchronization is performed when the basic frequencies of the respective system units or the respective oscillation circuits are different.
Further, in the case of the technique disclosed in the Japanese Patent Application Laid-open No. 2000-13217, synchronization is realized only when a phase difference exists between currents flowing respective oscillation circuits in the initial state. This is not so configured that synchronization is performed when the basic frequencies of the respective system units or the respective oscillation circuits are different.
Here, the basis frequency means a frequency that each system unit or each oscillation circuit oscillates independently when there is no coupling with other system units or oscillation circuits. Further, the oscillation circuit disclosed in the Japanese Patent Application No. 2000-13217 is limited to an oscillation circuit which is operative according to the van der Pol equation.
An object of the present invention is to provide reference vibration generators and their synchronizing method for realizing efficient synchronization among multiple system units so as to enable joint operation among system units arranged distributively, irrespective of the basic frequency of a reference vibration generator of each system unit. Another object of the present invention is to provide reference vibration generators and their synchronizing method which can be formed using not only oscillations according to the van der Pol equation but also using any limit cycle vibration.